The present disclosure generally relates to multi-beam interference lithography, and specifically to using variable neutral density filters and/or refraction cancelling prisms to improve interference exposure patterning on photosensitive film.
Multi-beam interference lithography (MBIL) utilizes multiple coherent, monochromatic beams of electromagnetic (EM) radiation, such as laser light superimposed against each other to create an interference pattern along multiple dimensions which can be used to expose photosensitive film (PR) to create complex patterns in a semiconductor fabrication process. However, traditional MBIL presents various shortcomings. First, due to the non-uniform distribution of power in the wave front of an interfering beam, the resulting photosensitive film pattern may not be exactly as desired. This is not ideal where precision and small feature sizes are required. Additionally, refraction between the air and photosensitive film interface limit the degree of slant at which the beams of EM radiation can be set at (depending on wavelength), and in turn limits the types of patterns that can be created. Hence, an improved means of MBIL is desired.